Neuroprotective effect of berberine is mediated by MAPK signaling pathway in experimental diabetic neuropathy in rats

The mechanisms leading to diabetic neuropathy are complex. As an active component in several traditional Chinese medicines, berberine has a beneficial effect in the treatment of diabetes with hyperlipidemia. This study evaluated the protective effects of berberine on diabetic neuropathy induced by streptozotocin and a high-carbohydrate/high-fat diet in rats. Diabetic neuropathy was induced in rats by intraperitoneal injection of 35 mg/kg streptozotocin and a high-carbohydrate/high-fat diet. Two weeks after diabetes induction, rats were treated with berberine (100 mg/kg) and rosiglitazone (4 mg/kg) for 24 weeks. Rats were studied using evoked potentials, the Morris water maze, transmission electron microscopy, real-time PCR, and Western blotting. Blood glucose, glycated hemoglobin, lipid profile, body weight, evoked potentials, and memory were altered in diabetic rats, as was the hippocampal expression of neuritin mRNA, p38 mitogen-activated protein kinase mRNA, c-Jun N-terminal kinase (JNK) mRNA, extracellular signal-regulated kinase mRNA and the phospho-proteins of p38, JNK, and extracellular signal-regulated kinase. In diabetic rats, berberine decreased body weight and the blood levels of glucose, glycated hemoglobin, triglyceride, and total cholesterol, improved memory and affected evoked potential by decreasing latency. Berberine decreased the mRNA expression of neuritin, p38, and JNK and the protein expression of neuritin, p-p38, and p-JNK. Slight micropathological changes were observed in the hippocampus of berberine-treated diabetic rats. These findings suggest that berberine has a beneficial effect against diabetic neuropathy by improving micropathology and increasing neuritin expression via the mitogen-activated protein kinase signaling pathway.